Vertically polarized log-periodic antenna



p 1966 RICHARD F. H. YANG 3,271,775

VERTICALLY POLARIZED LOG-PERIODIC ANTENNA Filed July 25, 1963 2 Sheets-Sheet l p 1966 RICHARD F. H, YANG 3,271,775

VERTIGALLY POLARIZED LOGPERIODIC ANTENNA Filed July 25, 1963 2 Sheets-Sheet 2 United States Patent 3,271,775 VERTHCALLY POLARIZED LOG-PERIODIC ANTENNA Richard F. H. Yang, Orland Park, Ill., assignor to Andrew Corporation, Orland Park, Ill., a corporation of Illinois Filed July 25, 1963, Ser. No. 297,647 7 Claims. (Cl. 343-7925) This invention relates to antennas and more specifically to antennas of the construction known as logarithmically periodic, now commonly known as log-periodic.

Log-periodic antennas are now in fairly common use for a variety of purposes where performance over a wide frequency range is required. The construction in most common use is a dipole employing a pair of tapered or triangular plane radiating portions, each comprising a set of conductor elements having a straight stem conductor extending from the apex or vertex of the triangle, along the center-line, with conductors'extending from this centerline or stem conductor, alternated on either side thereof in the plane of the element, these extending conductors or poles of the antenna being of increasing length with in-' creasing distance from the vertex, thus forming the generally triangular element. The width (dimension along the stem) of each of these extending conductors or poles is also correspondingly tapered. In general, there are em-' ployed two elements or half-portions of this description, fed in opposite phase at the apexes of the triangles. The triangular half-portions are normally complementary and the half-portions extend from the feed region in a generally symmetrical manner, i.e., such that their respective planes are perpendicular to the plane formed by the centerline or stem conductors, with a greater or lesser angle between the planes depending upon the particular purposes of various designs, notably desired directional characteristics. A simple form of log-periodic antenna employs a single pair of such half-portions, closely spaced and parallel. Although the theory, which is by now well known, is somewhat more complex, such a structure may be considered to resemble a series of dipoles, each for a different frequency, extending from an open-wire transmission line formed by the two stem portions. Such dipoles may of course be used in a variety of arrays or stacks for various specialized purposes, particularly as regards directionality. The direction of polarization is of course the direction of extension of the poles.

Details of techniques of construction of such antennas of course vary over a great range, both as regards features of construction particularly applicable to this type of antenna and as regards features of construction which are common to other types of antennas. As regards the former, there are many variants, for example, of shapes and types of extending poles, including more or less rectangular teeth, triangular teeth, and others which have been developed and used. As regards constructional fea tures which vary in a manner more or less common to all antennas, many constructional features are of course a function largely of practicality at any given frequency range. Thus at high frequencies, such dipoles may be, for example, printed or similarly deposited on plastic sheets, while at low frequencies the construction may involve the stringing of long wires, guying, poles, and similar constructions.

The logarithmic dipole encounters severe construction difficulties where the lower end of its frequency band extends down to frequencies such as a few megacycles, where at lower frequencies.

3,271,775 Patented Sept. 6, 1966 vertical polarization is employed, as is common in com munication systems. The base of the triangular configuration is essentially a half wavelength at the lowest frequency of operation, and accordingly is required to extend hundreds of feet in height. The direction of maximum radiation of such an antenna is of course in the plane of the stem or center-line conductors, so that even the apex or feed portion must be elevated to about half this distance. Such structures become almost prohibitive in size, and there have accordingly been attempts made heretofore to design logarithmic periodic antennas more suitable for use with vertical polarization at low frequencies than the simple dipole. By analogy to the various quarter-wave vertical-radiator structures used in narrow-band or conventional structures, these employ configurations with a maximum height of a quarter-wave, rather than a half-wave, at the lowest frequency of operation, with the lower half of the usual dipole replaced by some structure serving the general function of a groundplane or counterpoise. Such structures in general have heretofore used separate counterpoise constructions precisely spaced below the radiating elements or have used lumped-constant circuit elements connected to earth, properly adjusted in value, to produce the desired efliciency of radiation.

Although constructions of the type just mentioned heretofore known are satisfactory in some instances, there are many applications in which they are far from satisfactory. This is particularly the case in so-called transportable systems, designed for quick and simple construction and use in communications systems. Antennas for such use, such as those employing telescoping towers or masts supporting a network of wires and supporting cables, with appropriate insulators, are not desirably extremely critical in their exact location with respect to the earth or to a separate counterpoise structure, nor is it desirable to incorporate lumped-constant couplings, tunable or otherwise, in making each installation.

The present invention stems from the seeking of a suitable log-periodic structure capable of simple and easily installed transportable use in vertical polarization orientation, without substantial addition to cost or complexity. As will hereinafter be seen, the novel construction of the invention fulfills this initial. purpose, and in addition will find many other utilities where antennas of the same general characteristics and performance are desired.

The general construction of the present invention may be easily described in terms of a conceptually simple type of modification of a log-periodic dipole of the above type which is of any conventional practical construction details. Practical dipole constructions in common use of course, as in other antennas, deviate in appearance from the exact construction described above, representing the constructional details of early or classic log-periodic dipoles. For example, it will readily be recognized that the parallelism in closely spaced planes is merely a convenient construction for high-frequency use, the spacing being required only as regards the transmission-line portion, and the radiating poles being properly considered as effectively co-planar, and being actually so constructed Likewise, exact parallelism of the transmission-line pair is not required where the spacingchange along the length is small at the frequencies involved. Variations like this in basic dipole constructions will be seen to be immaterial as regards the present invention. If the lower half of each half-portion of a vertically oriented logarithmic dipole is bent outwardly to a substantially horizontal position, it has been found in accordance with the present invention that the resultant structure may be placed very closely above another surface, such as the earth, and produce a radiation pattern sufiiciently similar to that of a dipole to be fully satisfactory, with substantially complete independence of the characteristics of, or exact spacing from, the surface below. As will readily be seen, these performance characteristics are generally similar, with relation to those of a logarithmic dipole, to the performance characteristics of a ground-plane or monopole single-frequency antenna, so that the vertically extending portion may be considered as the log-periodic equivalent of a vertical quarter-wave radiator, while the horizontally extending portion may be considered as roughly equivalent to the ground rods employed in the formation of a conventional ground-plane used with a tuned radiator. The horizontal portion may thus be conventiently referred to as the ground-plane portion as a matter of convenience of description; however, as will be observed from study, the analogy is not basically accurate as regards the theory of operation which underlies the experimental results. The exact theory is of course unknown, but it is presently believed that each horizontal conductor acts in a manner similar to the operation of a tuned counterpoise when the corresponding vertical conductor on the opposite half-portion is active because of the particular frequency of operation, the phasing of the feed to the respective elements being the same as the opposite phasing of, for example, a coaxially fed ordinary monopole because of the maintenance of the opposite phase of signals travelling along the open transmission line formed by the opposed stem portions.

There is also provided by the invention, further increasing the utility and convenience of the antenna, a novel type of feed which permits simple changing of the input impedance of the antenna described to permit, when desired, feeding of an array of such antennas, or a single antenna, with a line of the same impedance. There are provided auxiliary conductors paralleling the conductors of the transmission line formed by the stern conductors, which may be selectively connected and disconnected to alter the impedance. Provision is made for such connection and disconnection at the discrete points which are found to be necessary to have the multi-conductor line act in a manner which is more or less analogous to changing the spacing of the half-portions of the antenna.

The more basic teachings of the invention are generally described above, and many embodiments may readily be constructed from what has already been said. However, in its narrower aspects, the invention may best be understood from the description of the particular embodiments and modifications illustrated in the drawing and described below.

In the drawing:

FIGURE 1 is a view in perspective of a log-periodic antenna made in accordance with the invention;

FIGURE 2 is a schematic view illustrating the antenna as located slightly above the surface of the earth;

FIGURE 3 is a more or less schematic view illustrating a transmission-line or feed construction for varying the impedance of the antenna;

FIGURE 4 is a fragmentary view illustrating a constructional detail of an antenna such as that of FIG- URE 1, modified in constructional detail for use in transportable form;

FIGURE 5 is a sectional view taken along the line 55 of FIGURE 4; and

FIGURE 6 is a perspective view of the feed portion of the antenna of FIGURES 4 and 5.

Referring first to FIGURE 1, the antenna there illustrated is of the logarithmic periodic ype wherein the conductors extending from the stem portions 14 and 1-6 are in the form of wire triangles. In the illustrated antenna, the vertical portion 18 is identical with the top half of an ordinary form of vertically oriented log-periodic dipole, the triangular extensions 20, 20a, 2012, etc. from stem portion 14 being in complementary locations to the triangular extensions 22, 22a, 221:, etc. on stem portion 16. The additional triangular extensions which would be below the stem portions 14 and 16 in a vertically oriented dipole, however, are replaced by triangular extensions 24, 24a, 24b, etc. extending horizontally outward from stem 14, and by triangular extensions 26, 26a, 26b, etc. similarly extending from stem 16. The sizes of these triangular extensions are sucuessively tapered in the manner well known in design of logarithmic periodic antennas, and the overall structure is thus that which is obtained by bending upward and outward the entire lower portions of the two members or elements forming a log-periodic dipole of the well known zig-zag construction, in which the half-portions are formed by a zig-zag wire defining a generally triangular area, with the stem conductor extending along the center-line. As a result, it will be seen that the pairs of extensions, such as 20b and 26b, which are the members of a dipole pair in the log-periodic dipole analog are here mutually perpendicular.

As shown in FIGURE 2, the antenna of FIGURE 1 may be disposed fairly closely above the earth, and is found to give highly acceptable isolation of the earth (or other conductors beneath the horizontal ground-plane portion), while producing a fully acceptable and desirable radiation pattern, with VSWR characteristics generally comparable to that of the correspond-ing dipole.

A zig-zag antenna of the construction illustrated in FIGURE 1, used as a scale prototype for experimental use in a design for lower frequencies, was constructed with an apex angle of 55 degrees and a periodic ratio of 0.81 (these of course being the same design parameters as used in the design of the dipole from which the construction is derived). The length of the antenna was 0.67 wavelength at the lowest frequency of operation. A gain of 7 db over an isotropic radiator was obtained over a 6 to 1 frequency range, with a tapering off to 5 db when the frequency was dropped to one-tenth of the highest frequency. A beamwidth of 70 degrees was obtained at frequencies just above the lowermost in the vertical plane, and degrees in the horizontal plane. Measurements of horizontal-polarized fields showed little or practically no power radiation from the portion serving as the ground plane.

As earlier indicated, the invention was primarily induced by the seeking of a suitable construction for a transportable antenna. Substantial utility is added to such an antenna by the ability to selectively use a single antenna or two antennas without the necessity of changing the coaxial cable or other feed. In FIGURE 3, there is shown a construction which is provided for the purpose of changing the impedance of the antenna of FIGURE 1 without disturbing the basic structure, so that the antenna may readily be converted as to impedance for proper matching of the same feed by either a single antenna or a plurality of parallel-connected antennas. As there shown, additional wires or similar conductors 28 and 30' are disposed in spaced relation to the stern conductors 14 and 16. By selectively connecting and disconnecting these auxiliary conductors to the respective stem conductors 14 and 16, the impedance of the antenna can be varied. As may be seen in FIGURE 3, the conductor 28 is here connected to the conductor 14 by shorts or jumpers 3-2; as indicated at 34, additional shorts or jumpers may be installed or removed at each of the places where the wires forming the elements 22, etc. and 26, etc. contact the stem conductor 16, connections at these points being the full equivalent for practical purposes of making both wires 30' and 16 effectively a single conductor for all purposes as regards the transmission line action of the stem conductors, and the jumpers 32 may be permanently installed at the same locations along the conductor 14. Connection and disconnection of the jumpers thus varies the impedance in the same manner as would substituting stem conductors of different size.

FIGURE 4 shows the manner in which the antenna of the invention may be constructed for field transportable use, employing the techniques of stringing of insulators and wires, commonly used in the large-dimension lowfrequency versions of antennas of any type in substitution for the rigid unitary type of mechanical assembly exemplified in FIGURE 1. As here shown, wires 36 and 38 are strung through eye-apertures 40 and 42 in an insulator 44, which may be one of a string of such support insulators strung along a line slightly above the ground. Each wire 36 and 38 may be a unitary wire strung vertically and horizontally to form one respective half of the large-scale (low-frequency) equivalent of the soldered-wire type of construction employed in forming the triangular extensions in the mechanical construction shown in FIGURE 1.

As seen in FIGURES 4 and 5, the transportable or knockdown construction uses a two-wire open transmission line which is oriented slightly differently from the classic logarithmic dipole construction used at higher frequencies, where the transmission line portion of the assembly is less negligible in transverse dimensions as compared to any wavelength and to the other portions, so that more complete symmetry is required. As shown in FIGURE 4, the transmission line or stem conductors 46 and 48 are vertically oriented with respect to each other and connected to the respective conductors 36 and 38 forming the log-periodic half portions, by jumpers 50 and 52. It will be of course understood that the illustrations of FIGURES 4 and 5 are largely schematic, and that the jumpers 50 and 52 are actually connectedby suitable clips or clamps which are of any of the various constructions commonly used in the analogous details of other transportable antenna types.

As seen in FIGURE 5, additional conductors 54 and 56 extend parallel with the transmission line conductors 46 and 48, in a manner analogous to the relation of the conductors 28 and 30 to the stem conductors 14 and '16 (except, of course, for the 90 degree rotation as compared with FIGURE 3, which is electrically immaterial in the low-frequency construction). Below these open-wire conductors is a coaxial line 58. The entire assembly of conductors 46, 48, 54, and 56, and coaxial line 58 is supported and held in relative orientation by a series of insulating blocks 60.

In FIGURE 6 is shown the portion of the feed assembly at the front (small) end of the antenna where the coaxial feed line which runs from the back (large) end is connected. As seen there, the assembly of conductors described terminates at the front surf-ace of a terminal insulator block 62, the inner conductor 64 of the coaxial line 58 .being connected at 66 to one of the coaxial line conductors 46, and the outer conductor 68 of the coaxial line being connected to both of the wires 48 and 56 at 70.

Jumpers or shorting bars shown at 72 and 74 are used for the selective connection and disconnection of the wires 46 and 54, as discussed above.

Although best results are obtained with the horizontal extensions 24, 240, etc. and 2-6 and 26, etc. actually horizontal, i.e., perpendicular to the vertical radiators, these may be dropped by a substantial angle toward the vertical without great impairment of performance. Substantial advantage is obtained at angles of 30 degrees or more with respect to the vertical, although the 90 degree angle illustrated is greatly preferred in the particular use of the antenna described above.

Many modifications are of course possible. Although the particular logarithmic dipole construction illustrated in two forms, i.e., the zigzag conductor formation of triangular extensions, has the advantages of convenience and simplicity, as in any log-periodic antenna, any other of the known forms of log-periodic dipoles of the same 6 general overall type may readily be adapted to use with the present invention. Furthermore, since the symmetry between the radiating portions and the ground-plane portion is not as critical as in the case of the dipole from which the construction is derived, under certain conditions the formation of the horizontal poles or extensions may be desirably slightly different from that of the vertical poles or extensions. Also, for certain purposes it may be desirable to duplicate the ground-plane construction on both sides of each stem conductor, thus providing, in essence, complete symmetry of the ground-plane. However, it must be noted that such a construction must employ horizontal elements extending to both sides connected to the same stem conductor, not to the opposite stem conductors, since the phase relationship between the radiating portion and the ground-plane portion must be maintained.

Many other modifications, some obvious and others apparent only after study, will be made in employing the basic teachings of the invention. Accordingly, the scope of the protection to be afforded the invention should not be limited to the particular embodiments illustrated in the drawing and described above, but should be determined solely by reference to the appended claims.

What is claimed is:

1. A log-periodic antenna having:

(a) an open-wire transmission-line pair,

(b) vertically disposed conductor elements of logperiodic dimensions and spacing extending upward along the transmission-line pair,

(c) alternate upwardly extending conductor elements being connected to respective members of the transmission line and said upwardly extending elements being the sole vertically disposed elements,

(d) and conductor elements of log-periodic dimensions and spacing each extending in only one at least par tially horizontal direction from the transmissionline pair, the horizontal component of said outward extension of successive elements being alternated in direction,

(e) the latter conductor elements each being connected to the transmission-line member opposite that to which the vertically disposed conductor element in the corresponding position along the transmission line is connected.

2. The antenna of claim 1 wherein the outward-extending elements are fully horizontal.

3. The antenna of claim 1 having at least one conductor extending parallel to the transmission-line pair and means to selectively connect and disconnect said last conductor with and from one of the members of the pair at points along its length to alter the impedance of the antenna.

4. The antenna of claim 1 having a coaxial transmission line extending parallel with the open-Wire pair, and having its inner and outer conductors connected to the respective members of the pair at the feed end of the antenna.

5. A log-periodic antenna comprising a log-periodic dipole of the type consist-ing essentially of conductor elements of log-periodic dimensions and spacing extending generally symmetrically from a center-line and stem conductors extending along the center-line and connected to alternate conductor elements on the opposite sides of the center-line to form oppositely phased complementary half-portions, the conductor elements on one side of the center-line being substantially co-planar, and the conductor elements on the other side of the center-line extending outward in alternated opposite directions at equal angles of at least 30 degrees from the plane of the conductor elements on the first side 6. The antenna of claim 5 wherein the elements so oppositely extending are perpendicular to the plane of the elements on said one side of the center-line to form a single plane perpendicular to the tfirst plane.

7. In combination with an antenna of the type having a pair of conductors extending along its length and forming an open-wire balancedtransmission line, and radiating elements spaced along the line and connected to the respective members of the pair, additional conductors extending parallel with the transmission line pair and means at each point of connection of a member to the radiating elements to selectively connect and disconnect one of the additional conductors and one of the members of the pair to alter the impedance of the antenna.

References Cited by the Examiner UNITED STATES PATENTS 8 3,113,316 12/1963 Berry 343792.5 3,165,748 1/1965 Woloszcuk 343-792.5 3,179,943 4/1965 Buzbee 343792.S

FOREIGN PATENTS 674,128 11/ 1963 Canada.

HERMAN KARL SAALBACH, Primary Examiner. R. F. HUNT, Assistant Examiner. 

1. A LOG-PERIODIC ANTENNA HAVING: (A) AN OPEN-WIRE TRANSMISSION-LINE PAIR, (B) VERTICALLY DISPOSED CONDUCTOR ELEMENTS OF LOGPERIODIC DIMENSIONS AND SPACING EXTENDING UPWARD ALONG THE TRANSMISSION-LINE PAIR, (C) ALTERNATE UPWARDLY EXTENDING CONDUCTOR ELEMENTS BEING CONNECTED TO RESPECTIVE MEMBERS OF THE TRANSMISSION LINE AND SAID UPWARDLY EXTENDING ELEMENTS BEING THE SOLE VERTICALLY DISPOSED ELEMENTS, (D) AND CONDUCTOR ELEMENTS OF LOG-PERIODIC DIMENSIONS AND SPACING EACH EXTENDING IN ONLY ONE AT LEAST PARTIALLY HORIZONTAL DIRECTION FROM THE TRANSMISSIONLINE PAIR, THE HORIZONTAL COMPONENT OF THE SAID OUTWARD EXTENSION OF SUCCESSIVE ELEMENTS BEING ALTERNATED IN DIRECTION,
 7. IN COMBINATION WITH AN ANTENNA OF THE TYPE HAVING A PAIR OF CONDUCTORS EXTENDING ALONG ITS LENGTH AND FORMING AN OPEN-WIRE BALANCED TRANSMISSION LINE, AND RADIATING ELEMENTS SPACED ALONG THE LINE AND CONNECTED TO THE RESPECTTIVE MEMBERS OF THE PAIR, ADDITIONAL CONDUCTORS EXTENDING PARALLEL WITH THE TRANSMISSION LINE PAIR AND MEANS AT EACH POINT OF CONNECTION OF A MEMBER TO THE RADIATING ELEMENTS TO SELECTIVELY CONNECT AND DISCONNECT ONE OF THE ADDITIONAL CONDUCTORS AND ONE OF THE MEMBERS OF THE PAIR TO ALTER THE IMPEDANCE OF THE ANTENNA. 